Based on the shape of a battery case, a secondary battery, the demand for which has increased in recent years, may be classified as a cylindrical battery having an electrode assembly mounted in a cylindrical metal can, a prismatic battery having an electrode assembly mounted in a prismatic metal can, or a pouch-shaped battery having an electrode assembly mounted in a pouch-shaped case made of an aluminum laminate sheet. The cylindrical battery has advantages in that the cylindrical battery has relatively large capacity and is structurally stable.
The electrode assembly mounted in the battery case serves as a power generating element, having a cathode/separator/anode stack structure, which can be charged and discharged. The electrode assembly may be classified as a jelly roll type electrode assembly configured to have a structure in which a long sheet type cathode and a long sheet type anode, to which active materials are applied, are wound in a state in which a separator is disposed between the cathode and the anode or a stacked type electrode assembly configured to have a structure in which a plurality of cathodes having a predetermined size and a plurality of anodes having a predetermined size are sequentially stacked in a state in which separators are disposed respectively between the cathodes and the anodes. The jelly roll type electrode assembly has advantages in that the jelly roll type electrode assembly is easy to manufacture and has high energy density per weight.
In connection with the above, a vertical sectional perspective view of a conventional cylindrical battery is typically shown in FIG. 1.
Referring to FIG. 1, the cylindrical battery 100 is manufactured by mounting a jelly roll type (wound type) electrode assembly 120 in a cylindrical can 130, injecting an electrolyte into the cylindrical can 130, and coupling a top cap 140 having an electrode terminal (for example, a cathode terminal, which is not shown) to the upper end, which is open, of the cylindrical can 130.
The electrode assembly 120 is configured to have a structure in which a cathode 121 and an anode 122 are wound in a circle in a state in which a separator 123 is disposed between the cathode 121 and the anode 122. A cylindrical center pin 150 is fitted in the core of the electrode assembly 120 (the center of the jelly roll). The center pin 150 is generally made of a metal material to exhibit predetermined strength. The center pin 150 is configured to have a hollow cylindrical structure formed by rolling a sheet type material. The center pin 150 serves to fix and support the electrode assembly. In addition, the center pin 150 serves as a passage to discharge gas generated due to internal reaction of the battery when charging and discharging the battery and when operating the battery.
In recent years, however, a problem related to heat generated from the secondary battery due to high-performance operation of the secondary battery has become more serious.
Heat generated from the secondary battery causes decomposition of a cathode active material and an electrolyte. As a result, a plurality of side reactions may rapidly progress and, in the end, the secondary battery may catch fire or explode.
It has been proved that such a phenomenon occurs at an electrode tab upon which current is concentrated during charge and discharge of the battery and, in particular, is serious for an anode tab.
A conventional anode tab is made of a single material, such as nickel, and has a single size. In order to solve the heat-related problem, the anode tab may be made of copper, which has lower resistance than nickel. However, it is difficult to secure easiness in welding between the anode tab made of copper and an electrode foil as a current collector or a battery case. For this reason, it is difficult to manufacture the anode tab using copper.
Therefore, there is a high necessity for technology to fundamentally solve the above problems.